This invention relates to colloidal clays in general and more particularly to a method of increasing the viscosity of such clays.
There are many clays which are found in nature. Basically, clay is a very fine grained, unconsolidated rock material which normally is plastic when wet, but becomes hard and stony when dry. Ordinary clay consists of hydrous silicates of aluminum, together with a large variety of impurities. Geologically, clay can be defined as a rock or mineral fragment, having a diameter less than 1/256 millimeter (0.00016"). This is about the upper limit of size of a particle that can exhibit colloidal properties.
Clays are widely used in the manufacture of tile, porcelain, as is well known and they are further used as filtering aids in oil and in other industrial processes. Clays are also used in drilling operations and are added to water, for example, to thicken the water or water solutions for these purposes and for other purposes as well. Particularly, colloidal clays are highly desirable in many industrial uses and the necessity of providing a colloidal clay is well known in the industry.
Colloidal attapulgite is mined in nothern Florida and southern Georgia and can be processed to give a colloidal grade of clay which is used to thicken water or water solutions for various industrial purposes. There are many techniques described and known in the prior art which operate to convert mined clay to its colloidal form. Certain examples of such techniques can be found by referring to U.S. Pat. No. 3,951,850 entitled "Conversion of Clay to its Colloidal Form by Hydrodynamic Attrition" issued on Apr. 20, 1976.
Essentially, attapulgite and sepiolite are unique in performance among the clay mineral thickeners. The uniqueness resides in the fact that in addition to the ability of these clays to thicken fesh water, they can also be used to thicken water solutions of salts that contain high concentrations of ionic materials.
Clays such as Wyoming bentonite are widely used gelling clays but have disadvantages. These clays will not swell and develop viscosity in the presence of flocculating cations or in low to medium ionic concentrations. For this reason attapulgite and sepiolite clays are often employed as thickening agents for saturated salt water drilling fluids. These fluids contain sodium and chloride ions. The clays can also be employed as thickeners in gypsum inhibited drilling fluids which contain calcium and sulphate ions as well as in suspension fertilizers that contain ions such as ammonium, phosphate, potassium, chloride, nitrate and sulfate. Essentially, these clays can be employed with substances or solutions having ionic types or concentrations that would interfere with the employment and use of the ordinary types of gelling grades of clay such as Wyoming bentonite, hectorite and so on.
Colloidal grades of attapulgite exhibit a considerable degree of variation in their viscosity-imparting characteristics. These variations are indicated by the amount of viscosity a given percentage of clay produces in any solution and how much stirring is necessary to produce the viscosity. In the oil well drilling industry these factors are commonly referred to as the yield in barrels of 15 centipoise mud per ton of clay (B/T) and rate of viscosity yield of the clay respectively. See API "Standard Procedure for Testing Drilling Fluids", API RP 93B 3rd Edition, February 1971 and API "Specification for Oil-Well Drilling-Fluid Materials", API Spec. 13A, Sixth Edition, January 1974. Many theoretical reasons have been offered to account for the above description variations but none have been proven.
It is established practice to improve the rate of yield and sometimes the yield of the clay by subjecting the clay to extrusion during the processing operations. Certain of the crude clays exhibit improvements in yield and rate of yield when additives such as magnesium hydroxide, Mg(OH).sub.29 or hydrated MgO are pugged into them prior to extrusion. In spite of this, very few crude clays exhibit a yield improvement when the above noted additives are post added to a finished product.
The post addition of chemical hydrate lime, Ca(OH).sub.2, results in a considerable improvement in yield and a minor improvement in rate of yield. Colloidal clays treated with Ca(OH).sub.2 are inherently unstable because of the possible air carbonation of the hydrated lime and the reaction of the hydrated lime with the clay. For the abovementioned reasons, lime additions followed by pugging and extrusion degrade the yield of the clay and when hydrated lime is post added, a uniform, intimately intermixture produced by grinding also drops yields. The recommended method of addition is to add the hydrated lime as discrete, easily discernible particles. This technique results in a very poor mixture. Furthermore, to avoid carbonation during storage, the finished, hydrated lime-treated product must be packaged in plasticlined bags.
The above outline represents the current state of manufacturing practice. It should be noted that in spite of the deficiencies of hydrated lime treatment, it is by far the most economical yield improvement method because of the much higher costs of pugging in hydrated MgO plus extrusion practices. In short, the most economically attractive treatment for yield improvement has to be the post addition of an inexpensive chemical additive.
It is therefore an object of the invention to provide a chemical additive which when post added to a colloidal clay substantially increases the yield factors, while further providing improved stability. The additive which is preferably unslaked lime, can be added rapidly and economically.